A Comparative Study of the le Conte's and Sharp-Tailed Sparrows

Abstract

MANY ecologists believe that interspecific competition will result in the elimination of one of the competing species or in the evolution of differences that will let the two species coexist without competing (Lack, 1954, 1966; Mayr, 1963). This has stimulated considerable study of the ecology of sympatric species. Ecologists studying avian populations seem convinced that food is the limiting resource of many populations, and they have focused attention on differences in morphological and behavioral adaptations associated with foraging. Sympatric species usually occupy different habitats or, if not, differ in overall size, in shape or size of bill, or in foraging habits (Lack, 1944, 1954). Many recent studies seem to support the original generalizations. The subjects of the present study are the Le Conte's Sparrow (Ammospiza leconteii) and the Sharp-tailed Sparrow (Ammospiza caudacuta). The latter is not only sympatric with the Le Conte's Sparrow in interior North America but also with the Seaside Sparrow (Ammospiza maritima) along the Atlantic coast. A comparison of the relationships between the Seaside and Sharp-tailed Sparrows (Woolfenden, 1956) with those between the Le Conte's and Sharp-tailed Sparrows might show how its sympatric relatives have influenced selection in the wide-ranging Sharptailed Sparrow.